1. Field of the Invention
The present invention relates to a display panel having a multilayer structure including a colored glass layer and a non-colored glass layer and to a process for manufacturing the display panel.
The display panel utilizes a structure having a glass layer with a coloring agent disposed on the inner face of a substrate as a stripe-like or a grid-like light shield member for enhancing contrast or a filter for color reproduction.
2. Description of the Prior Art
An AC type gas discharge display panel (i.e., a plasma display panel) has a dielectric layer that insulates electrodes arranged on the inner surface of the substrate from the discharge space. In general, the dielectric layer is made of a low melting point glass and is spread over the whole screen uniformly. The colored glass layer of a predetermined color is overlayed by the dielectric layer (as an under coat, for example). Namely, a multilayer structure including a colored glass layer and a non-colored glass layer is formed on the substrate. A thick layer method is used for forming the multilayer structure, in which glass paste is coated and burned.
The dielectric layer is preferably burned at the temperature substantially higher than the softening point of the glass material. However, if it is burned at the temperature approximately 100 degrees centigrade higher than the softening point, flow of the glass may cause a pattern collapse of the colored glass layer, diffusion of the coloring agent into the dielectric layer resulting in deterioration of transparency of the dielectric layer, or color change of the coloring agent resulting failure in obtaining desired coloring effect. Therefore, conventionally, the composition of the glass material of the dielectric layer is selected so that the softening point becomes a relatively high temperature (e.g., 570 degrees centigrade), so that the burning is performed at a temperature (e.g, 590 degrees centigrade) that is near to the softening point. In addition, in order to obtain a good dielectric layer, a thin dielectric layer is formed on the colored glass layer using a glass material having high softening point, and then, a material having low softening point (e.g., 490 degrees centigrade) is used and is burned at substantially high temperature so that the dielectric layer having a necessary thickness can be formed. The thin dielectric layer can prevent the deformation of the colored glass layer and the diffusion of the coloring agent.
There is another problem if the electrode is made of a transparent conductive material (ITO, NESA). Namely, a metal oxide added as a coloring agent degenerates and causes the color change or fading of the colored glass layer. One of the methods to solve this problem is disclosed in Japanese unexamined patent publication No. 9-1 29142. The method includes the steps of providing a gap for preventing color change between the transparent electrode and the colored glass layer, and mixing an oxidation agent into the colored glass paste.
If the dielectric layer is formed by the method explained above in which the glass material is burned at the temperature that is close to the softening point, leveling and defoaming process in the softened state can be insufficient so that the surface layer becomes rough with many foams. This layer has little transparency and deteriorates the intensity. The method of coating the thick dielectric layer over the thin dielectric layer can improve the transparency but has a disadvantage in its low productivity since two burning steps are required. In addition, two materials are necessary for the dielectric layer.
Furthermore, in order to avoid the color change and the color fade, the method of providing the gap for preventing color change has a strict limitation for the arrangement pattern of the colored glass layer, while the method of adding the oxidation agent is limited to a special coloring agent.
The object of the present invention is to provide a display panel that has a multilayer structure including a colored glass layer with a predetermined shape and optical characteristics and a non-colored glass layer with a high transparency, and is superior in productivity.
In the present invention, a crystallization glass that can be crystallized in the temperature lower than the softening point of the non-colored glass material is used as a material of the colored glass layer. The shape of the colored glass layer can be maintained even if the non-colored glass material is softened by crystallization. In addition, since the coloring agent is closed in the crystal, it is not diffused into the non-colored glass layer, and chemical change is hard to occur due to the heat. Therefore, the colored glass layer and the non-colored glass layer can be burned simultaneously for improving the productivity.
According to a first aspect of the present invention, a gas discharge display panel is provided that has a structure including transparent electrodes arranged on the inner surface of one of substrates and a non-colored glass layer between a discharge space and the transparent electrodes. The display panel has a colored glass layer that includes crystallization glass containing coloring agent and contacts the non-colored glass layer.
According to a second aspect of the present invention, the colored glass layer contacts both the transparent electrode and the non-colored glass layer.
According to a third aspect of the present invention, the colored lass layer is a light shielding layer containing the coloring agent selected from the group of iron monoxide (FeO), dichrome trioxide (Cr2O3), copper monoxide (CuO), nickel oxide (Ni2O3), cobalt oxide (CoO) and manganese dioxide (MnO2).
According to a fourth aspect of the present invention, the colored glass layer is a reflecting layer containing the coloring agent selected from the group of titanium dioxide (TiO2), aluminum oxide (Al2O3), silicon dioxide (SiO2), barium sulfate (BaSO4), barium titanate (Ba2TiO3), and mica isinglass.
According to a fifth aspect of the present invention, the colored glass layer is a filtering layer containing the coloring agent selected from the group of chromium oxide and cobalt oxide.
According to a sixth aspect of the present invention, a process for manufacturing a display panel is provided, which has a non-colored glass layer and a colored glass layer that contacts the non-colored glass layer. The process includes the step of forming a multilayer structure that includes a colored paste layer and a non-colored paste layer. In the colored paste layer, crystallization glass that is crystallized at the temperature TA and coloring agent are diffused. In the non-colored paste layer, glass powder having softening point that is the temperature TB higher than the temperature TA is diffused. The process also includes the step of heating and burning the multilayer structure to the temperature TC that is higher than the temperature TB and is lower then the softening point of the crystallization glass powder after the crystallization, so as to form the non-colored glass layer and colored glass layer simultaneously.
According to a seventh aspect of the present invention, the heating and burning step of the multilayer structure includes the step of setting the temperature gradient of the crystallization temperature range from the temperature lower than the temperature TA to the temperature TA smaller than the temperature gradient of the temperature range from the temperature TB to the temperature TC.
According to an eighth aspect of the present invention, the temperature difference between the temperature TB and the temperature TC is set to a value more than 50 degrees centigrade.
According to a ninth aspect of the present invention, the crystallization glass powder has a softening point that is higher than the temperature TB after the crystallization by 100 degrees centigrade or more.